The present invention relates to N,N'-bis (5-isocyanatonaphthyl)urea obtainable by reaction of naphthalene-1,5-diisocyanate ("NDI") and water in an inert solvent. The urea according to the invention, which may optionally contain a small amount of oligomeric ureas, may be used with advantage in the synthesis of polyurethane or polyurea elastomers.
It is known that monoisocyanates react with water to form N-substituted carbamic acid derivatives which can be converted into urea derivatives by reaction with more isocyanate in a reaction accompanied by elimination of carbon dioxide. Polyureas are similarly obtained from diisocyanates and water by polyaddition.
It is also known that, provided certain reaction conditions are maintained, it is possible to obtain a low molecular weight urea diisocyanate corresponding to the following general formula ##STR1## by allowing 1 mol of water to react with at least 2 mol of a diisocyanate in a solvent at temperatures of from 0.degree. C. to 30.degree. C. As described in DAS No. 1,101,394, this reaction can only be carried out with diisocyanates which, like 2,4-tolylene diisocyanate, for example, contain isocyanate groups of different reactivities.
According to U.S. Pat. No. 2,757,185, compounds such as meta- or para-phenylene diisocyanate form only polymeric and not monomeric ureas when reacted with water.
It has now surprisingly been found that N,N'-bis(5-isocyanatonaphthyl)urea, which optionally contains only a small amount of oligomeric ureas, can be obtained in a high yield by reaction of naphthalene diisocyanate with water in a molar ratio of about 2:1 in inert solvents at a concentration of at least 2% by weight, based on the solvent used. A basic catalyst may optionally be used.
The urea according to the invention may be advantageously used for the production of polyurethane or polyurea elastomers.
In comparison with elastomers based on NDI, elastomers obtained using the urea according to the invention are characterized not only by excellent mechanical properties, but also especially by high thermal stability. By virtue of its high melting point, the urea according to the invention is also suitable as a heterogeneous isocyanate component in one-component systems according to DE-OS No. 3,230,757. Another advantage is that sublimation, which is a troublesome tendency when processing NDI in the melt, does not occur where the corresponding urea is used, thereby providing simple and safe handling.